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  #21  
Old 04-12-2017, 12:40 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
Either way would be better than what most folks are flying. Nigel and I talked to one ignition manufacturer at S&F who cheerfully admitted the curve in their system is a best guess, and I suspect that's common.

It's not crazy, or improper. Remember, even in the case of a certified ignition, the FAA's only interest is "Will it fail the engine?", not optimum performance.
I guess I find it interesting that in their attempt to remain solidly in the "conservative" camp (which I fully understand), some of those "best guesses" are actually too aggressive.
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  #22  
Old 04-12-2017, 07:21 PM
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Default Parallel Valve

Hi Dan,

My engine is a parallel valve IO-380 (a stroked IO-360 0.200") with 10:1.

Toolbuilder,

The curves in the graph in this thread are the peaks from the individual curves at a range of altitudes. At each condition I swept the timing from as little as 20 degrees to as much as 40 degrees. Short answer is that yes the graph is based on test. The curves for any one altitude and mixture condition were pretty flat and the difference between 20 degrees advance and say 30 degrees advance when ROP were pretty small, as in just a couple of knots. The original graphs are in the KitPlanes article if you want to see them.

The limitation of the PMag for someone looking to highly optimize their timing is the fact that the slope of timing as a function of MAP and RPM is locked. You can limit the maximum timing, but setting it at 40 degrees doesn't mean that a condition exists where you will ever get that much. Also if you think you have too much advance at high MAP and you use the advance shift function it slides the whole matrix so what you take off at high MAP you also take off at low MAP.

I also agree that curves from popular vendors all probably have too much advance at high MAP and they ramp in the extra timing quite aggressively as well. My test showed that you were much better off having a bit less advance than optimal rather than more than optimal. The gain was cooler CHT and better detonation margin, the cost was a very small speed and efficiency loss.

Sure would be nice to be able to set the MAP where extra advance is added and the rate at which it is added up to some maximum at a set MAP.

Cheers

Nigel
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  #23  
Old 04-18-2017, 09:22 AM
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William Slaughter William Slaughter is offline
 
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Hi Nigel,
As a result of this testing, how do you have your pmags set for normal operations? My engine is a virtual clone of yours, and I will need a starting point when we begin test flying later this year.
Thanks again for sharing all of your work with us.

William
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  #24  
Old 04-18-2017, 01:59 PM
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Default How I set my PMags

Hi William,

My set up is equivalent to timed at TDC with jumper in. Via the EICommander I also set the rev limit at 3072, max 35 deg advance and zero advance shift. I know putting in a negative shift will lower my CHT a little but I hate to loose efficiency in the cruise.

If you want to be conservative during the break in period when you are likely running at high power and ROP you could just use a lower max advance, say 25 degrees, to stop excessive advance increasing CHT. If you don't have an EICommander remember you can also change these settings with a laptop.

Cheers

Nige
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